1. The Field of the Invention
The present invention relates generally to optical subassemblies and associated components. More particularly, embodiments of the present invention concern an optical subassembly that includes a lens which facilitates the hermetic sealing of various components of the subassembly, while also implementing desired optical effects with respect to the optical signals transmitted and received by such optical components.
2. Background and Relevant Art
Transistor outlines, sometimes also referred to as a “TO” or “TO can,” are widely employed in fiber optic applications. A typical TO can includes a header that is enclosed by a housing having a window at one end. In some cases, the window is part of the housing, while in other cases, the window is a separate component positioned within an opening defined by the housing. In either case, the housing and window cooperate with the header to define a hermetic enclosure.
An optical device such as a laser diode or photodiode is positioned on the header within the hermetic enclosure so as to be able to transmit or receive, respectively, an optical signal by way of the window. In addition, one or more lenses are sometimes provided that are interposed between the optical transmitter, or optical detector, and the window so as to impart various optical effects, such as collimation and focusing, to a received or transmitted optical signal. In some TO can geometry, a lens can be mounted in place of the window of the TO can, and can be positioned relative to the optical transmitter or receiver. In yet other cases, the TO can is configured so that the lens, or lenses, are disposed outside the TO can.
Typical TO cans are configured to be received in a receptacle defined in a connector port. Opposite the TO can, the connector port includes or defines a receptacle configured to receive a connector ferrule. The connector ferrule, in turn, carries an optical fiber such that when the connector ferrule is fully received within the receptacle defined by the connector port, the optical fiber is optically coupled with the window, lens(es) and laser of the TO can. In this way, optical signals transmitted by an optical transmitter in the TO can are directed out onto the optical fiber. Likewise, incoming optical signals received over the optical fiber are directed to the optical detector disposed within the TO can, through the lens(es) within the port.
While TO cans and their associated components provide useful functionality in many cases, the typical TO can possess certain characteristics which can make it unsuitable and/or undesirable for use in some applications. By way of example, the use of multiple components in the construction of the TO can complicates manufacturing processes and also contributes to the relatively high cost of typical TO cans. In addition, the use of multiple parts results in a relative increase in the number of potential failure points in the final assembly, especially during shock and vibration. These failures can also be amplified by the range of temperatures to which the optical port is typically subjected. For example, the different optical components mounted within the mechanical port structure may move with respect to each other during operation as the support structure expands at higher temperatures.
Further, the configuration of typical TO cans does not make the TO can well suited to high volume production techniques such as wafer scale manufacturing. While some components of the TO can, such as the laser, can be produced with wafer scale techniques, the other components of the TO can must be produced with more labor intensive and time consuming techniques, and the same is likewise true with respect to assembly of the TO can.
Another concern with many TO can configurations relates to the lens and window arrangement. In particular, while the lens implements desired optical effects with respect to received or transmitted optical signals, the window should be an optically neutral element. That is, the purpose of the window is simply to allow the passage of optical signals into, or out of, the TO can, and to cooperate with the housing to facilitate formation of a hermetic chamber or enclosure for the optical transmitter or optical detector.
However, while the window is intended to be optically neutral, it is generally the case that every optical element placed in the path of an optical signal has at least some effect on that optical signal. Thus, while the window of the TO can is not employed to implement any particular effect with respect to the optical signal, the inclusion of the window as an additional optical element in the optical path can nonetheless act to compromise the integrity of optical signals transmitted and received in connection with the operation of the TO can and associated components.
Another problem associated with the window of the TO can is that it can place a limitation on the minimum distance the lens or lenses could be placed with respect to the laser and the detector. Since the output of the beam from an edge emitting laser grows (diverges) over this distance, the TO window and the lense(s) need to have a large enough pupil or aperture in order to effectively transmit all the light. As such, this can result in a needed increase in the size of the optical port as well.
Other complications can occur, such as in the case where a lens is incorporated on the TO can in place of the lens, which can result in fairly complicated alignment schemes. For example, any alignment of the lens on the TO lens cap to the laser or the detector on the TO header may still be compromised when the TO can is hermetically sealed. Thus, manufacturers that produce TO cans with lenses already aligned will often charge as much as double the lens cost for the TO assembly.
In view of the foregoing, and other, problems in the art, what is needed are optical subassemblies suited for construction using wafer scale techniques or other suitable high volume, low cost production techniques. Further, the optical subassemblies should be constructed so that the number of components required to build the optical subassembly is minimized. As well, the optical subassemblies should provide for a relative reduction in the number of optical components present in the optical path. Finally, the optical subassemblies should be suited for use with a variety of optical transmitters and optical detectors.